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18 Jul 2002

 

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Scanning Considerations

 

Computer SIG Meeting - 10 October 1998)
Doug Hay and Elizabeth Rodier

See also Computer Special Interest Group (SIG)

General Considerations

Scanners can be used for digitizing line drawings, clip art and photos or for converting text to editable files (called Optical Character Recognition or OCR).

Like everything else what to buy depends upon what you want to do with the scans:

  • for internet publishing a low resolution, cheap scanner is fine
  • for reproducing photos at the same size, a higher resolution scanner would be required
  • for enlarging photos, or picking heads from a group picture, a better scanner is necessary.

Prices range from $100 to well over $1000 (Cdn).

Types of Scanners

Handheld

No longer sold new. They do an adequate job for most normal uses. Scan to 400 dpi. The limitation is they only scan 4 inches wide. You must stitch successive scans together for larger originals.

Feeeder/Drum

Can be very small for portability. Sometimes combined with a fax and printer (about $800). They are usually only 24 bit color and are limited to single sheets.

Fixed Bed

These are the most versatile, able to scan book pages and anything you can lay on a glass sheet. Most have optional accessory to scan negatives or slides.

Precision/Resolution Issues

Bits of colour vary from 24 on lower priced models to 30 on intermediate and 36 on top of the line models. 30 bits is adequate for most jobs. 36 bits often doesn't cost much more and it will give you a difference in color density in the darker areas.

DPI or dots per inch is a measure of the detail. The dpi are quoted as optical/hardware and interpolated/enhanced. The optical is what is actually scanned. Software gives you an apparent to the eye enhanced image, but there is not any more detail. Optical varies from 300 to 600 dpi and enhanced resolutions are quoted as high as 9600.

If you are using a color printer, there is no use scanning at any greater than your printer's dpi. Often 100 dpi is high enough. Most printers print at an optimum dpi somewhere between 75 and 200. The size of your scanned file quadruples for every doubling of dpi. For instance a 4 x 6 color photo scanned at 100 dpi is 700 kb, 200 dpi is 2.8 mb, 400 dpi is 11.3 MB.

Installation

Scanners can be hooked by a SCSI board or parallel port. SCSI requires installation of a card in your computer and costs about $30 more than a parallel, but is significantly faster. A parallel connects directly to your printer port. Most have a port in the back to connect your printer to.

Prices

Prices vary from $100 to near $1000. A good solid performer should not be more than $400. The ones with the best reputations are:

Manufacturer Model Bits DPI Price (Cdn)
HP Scanjet 5100 36 bit 600 $380
Microtek E6PC 30 600 $420
UMax Astra 1200S 36 600 $360
Plustek 9636T 36 600 $300
Notes:
The Plustek does negatives and slides also.
The prices are list and there are often rebates available.
The lowest price one I have seen is the Storm EasyPhoto with 600 x 300 resolution at $112 (some people tell me it does a good job).

Software

Each scanner comes with all the software neccessary to scan, edit and store as well as OCR. The quality and complexity of software varies, but all will do an adequate job for a beginner. If you really get into it you can buy add-on software, the best of which may cost you more than the scanner. Photoshop for photo editing and Textbridge for OCR are the top sellers.

Hardware Demands

Because color scan files are so large, you should have at least 32 MB of RAM. (Cost about $50). You should have at least a 166 Mhz speed. Slower chips work OK but you might get tired waiting for them. Most scans will not fit on a 1.44 MEG floppy disk, unless compressed, so either a huge hard drive or an off-site storage such as a ZIP drive ($180) will be required if you do much scanning.

File Formats

There are 3 main types of file format:

  • TIF for continuous tones (photos) gives the best quality and maximum compatibility with other software. But they are the largest size.
  • GIF for line art and graphics this gives the best quality and a smaller size file.
  • JPG can give you great compression (up to 90 %) but you lose a little quality every time you compress or open the file. It won't work well for line art. For email or web pages it is almost a must because of the size.